In industries that rely upon access to subsurface geological strata in order to produce commercial flow streams, such as oil and natural gas, wells are drilled from the surface down to a planned depth using an assembled string of steel tubular pipe having a drill bit attached to the bottom of the string. As the string is rotated at the surface by a power train, the bit crushes rock and forms a wellbore of a diameter roughly the same as the drill bit. The rock fragments produced by this process, or cuttings, are carried out of the way of the bit by flowing a constant stream of mud, typically down through the center of the string, exiting the string at the bit, and back up through the annulus formed between the wall of the wellbore and the outer surface of the drill string pipe. As the mud flows up through the annulus, the viscosity of the mud is sufficient to exert a vertical force on the cuttings that overcomes the weight of the cuttings, and in this way they are carried up to the surface for processing and disposal. As long as the drilling is at or near a vertical direction, the viscosity forces are most effective because the direction of the flow of the mud is directly or nearly directly opposite to the gravity forces on the cuttings.
In horizontal drilling, after some vertical depth is achieved, the drill bit is then directed to an angle at or near horizontal, and may continue in that trajectory for great distances. The flow of the mud inside the wellbore is parallel with the axis of the wellbore, which in this situation is at or near horizontal, so the cuttings are not only carried horizontally by the viscous force of the mud, but are also acted upon vertically downward by the pull of gravity. The viscous forces imparted by the mud when travelling horizontally often cannot overcome the gravity forces, thereby allowing the cuttings to congregate in higher densities along the low side of the horizontal wellbore.
This accumulation of cuttings poses various problems for the drilling process. The higher density of cuttings there increases drag on the drill string by causing contact and interference with the rotational as well as translational movement of the drill string pipe and other drill string components. The higher density of cuttings also increases the wear and tear on the drill string, as well as increases the likelihood of downhole problems such as stuck pipe. All of these situations reduce the productivity of the drilling operation.
The subject matter of the present disclosure is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.